This invention relates to apparatus for frying foods and particularly to improved deep fat fryers wherein the fat is circulated and heated external to the fryer vessel.
Deep fat frying of foods such as potatoes, meats, fish, and pastries is performed by immersing the foods in a vessel containing heated cooking oil or fat. Of considerable importance in such fryers are their systems for heating the fat and for maintaining its temperature uniformity and cleanliness.
Heating systems of deep fat fryers are generally of three types. Some heaters comprise gas-fired burner tubes or electric elements immersed in fat held within the fryer vessel. A second category of fryer heaters includes systems which apply heat to fat in the fryer vessel by exposing the vessel to combustion gases or the condensible vapors of a heat pipe working fluid. A third type of heater includes a heat exchanger external to the fryer vessel through which fat is circulated, sometimes after passage through a filter.
Present deep fat fryers have one or more drawbacks or undesirable aspects. For example, commercially available fryers have relatively low efficiencies and, if gas-fired, have high flue losses. Typical calorimetric efficiencies for available gas-fired fryers are in the range of 40-60 percent. Another potential drawback of known fryers is their low load capacity and hence low output of cooked food.
Fryers with immersion-type heaters may require large vessels and be difficult to clean. Their heating systems, as well as those utilizing external firing directed at the bottom and sides of a fry tank, may heat the fat non-uniformly and cause premature breakdown of the fat.
Prior art fryers which circulate fat for external heating also have drawbacks. They may utilize substantial energy in pumping the fat, particularly if a filter is included in the circulation system. Replacement or cleaning of filters in such units can be difficult and time-consuming, and clogging or blockage of the filters requires an immediate shutdown of the fryer. Also, the heat exchangers of such fryers may be difficult to drain and clean.
Accordingly, it is an object of the invention to provide a deep fat fryer of high cooking efficiency.
It is a further object of the invention to provide a high efficiency deep fat fryer with external heating and continuous filtration of cooking fat.
Another object of the invention is a deep fat fryer which provides a high production output of cooked food.
Another object of the invention is to provide a deep fat fryer with continuous filtration and whose filtering system, if clogged, does not prevent continued operation of the fryer.
Another object of the invention is to provide a deep fat fryer with a heating system which has high efficiency and low flue losses, yet is quiet and reliable.
Another object of the invention is a deep fat fryer which provides circulation of cooking fat even when excess moisture is present in the fat.
Another object of the invention is to provide a deep fat fryer with continuous circulation of fat and with a simple, responsive control system for preventing overheating of fat during several possible conditions producing low flow rates of fat.